Mark Rein·Hagen (born 1964), often written as Mark Rein-Hagen, is a game designer who has contributed to role-playing games, card games, video games, and board games. He has contributed extensively to American gaming company White Wolf. He is perhaps best known as the creator of Vampire: The Masquerade and its associated World of Darkness games. He was also along with Jonathan Tweet one of the original two designers of Ars Magica.